This invention relates generally to coinjection molding and particularly relates to an improved apparatus for molding multi-layered articles which minimizes the effects of wall friction on contiguously flowing injection molding materials for supply to injection molding cavities.
As used herein:
xe2x80x9cFirst and second materialsxe2x80x9d is intended to cover at least two materials which are sequentially supplied to an injection mold, it being entirely possible that one or more other materials may be sequentially supplied before, between, or after the first and second materials;
xe2x80x9cBalanced Hot Runnerxe2x80x9d is a temperature controlled heated uninterrupted material conveying system extending from a single input (e.g. a material source or metering valve) to a plurality of outputs (e.g. metering valves or injection mold cavities) comprising a single passage branched into a plurality of passages with each of said plurality of passages, communicating with one of the plurality of outputs, for conveying material therethrough to simultaneously supply equal quantities of the material to each of the outputs;
xe2x80x9cUnbalanced Hot Runnerxe2x80x9d is a temperature controlled heated material conveying system, for the passage of material from an input (e.g. material supply source) to a plurality of outputs (e.g. metering valves for metering the material for supply of metered quantities of the material to injection mold cavities), which is not branched to provide passages of identical cross-section and length and does not divide the supplied material into equal quantities for the simultaneous supply of these quantities each to one of outputs.
The manufacture of pure, or virgin, resin preforms for blow molding containers is well known within the prior art. But since the advent of recycling, it is now possible to manufacture preforms with materials that are compositionally less pure than virgin materials. Such degraded, or recycled, materials not only yield positive environmental benefits in an ecologically fragile era but provide manufacturers with an alternative manufacturing method which allows for substantial reductions in costs.
But, since recycled materials are obtained from post consumer solid waste, certain new manufacturing problems have been encountered that were heretofore previously unknown. For example, manufacturers must now provide, at increased costs, additional equipment for keeping the virgin and recycled materials separate from each other. In addition, multi-layered articles, such as preforms, that are eventually used to form containers for food stuffs, have even further impediments by way of rigid statutory guidelines. The guidelines, enacted by the Food and Drug Administration (FDA), require that certain minimums must be met, or exceeded, before the containers can be approved as xe2x80x9cqualifiedxe2x80x9d to contain food stuffs and before the foods are allowed to be distributed to the consumer population. One extremely noteworthy FDA provision enacted theretowards provides for the assurance of product xe2x80x9ccleanlinessxe2x80x9d.
Currently, in order to meet the FDA cleanliness standards, a container must be configured such that only surfaces of virgin materials contact the foods and beverages therein. Other container surfaces, such as areas for contacting the human mouth, e.g. the dispensing orifice on a soda container, also require virgin material surfaces. As a result, it is economically desirable to provide manufacturers with a apparatus capable of utilizing recycled materials within containers while, at the same time, preventing recycled materials from contacting the very foods and liquids that are to be distributed to, and consumed by, the public.
Some advances towards the aforementioned goal have been attained by using coinjection molding techniques to manufacture multi-layered containers. The multi-layered containers thence produced have interior and exterior surfaces of the container comprised of virgin materials while the fill and support materials located within the interior of the container walls comprise the degraded, less than pure, recycled materials. Consequently, the economies and conservation of utilizing recycled materials is thereby achieved while simultaneously meeting the strict FDA statutory requirements.
Prior art coinjection molding techniques that produce the multi-layered containers described above, often first manufacture a multi-layered preform and then blow mold the preform into the final container. The formation of multi-layered containers are described in detail, for example, in Applicant""s U.S. Pat. Nos. 4,550,043 and 5,221,507.
Typically, the preforms are injection molded in multi-cavity molds which may have as many as 96 cavities. These preforms are then simultaneously produced by injecting appropriate amounts of a first and second material, i.e. virgin and recycled, into each of the cavities. To this end, the mold defines a manifold arrangement to convey the two materials to each of the singular cavities. Such an arrangement, as in Applicant""s prior patents, is known to convey each of the first and second materials into a singular hot runner before contiguously conveying the materials to the cavities. The combination then allows for a reduction in equipment costs due to the singular hot runner arrangement. The singular conduit repeatedly divides the materials flowing therein into a plurality of flow paths for delivery to each cavity and to thereby ultimately provide each cavity with a substantially equal amount of metered material at substantially the same temperature and at substantially the same time as every other cavity. Yet, with mold arrangements containing large numbers of cavities, such as with forty-eight and ninety-six cavities, the two materials contiguously flowing within a singular conduit have been known to have interface boundary problems between the virgin and recycled materials when conveyed over lengthy distances.
FIG. 1 illustrates potential interface boundary problems encountered with sequentially and contiguously flowing materials A and B in singular conduit 2. Flow is in the direction of arrow 4 with overlapping tails 6 lagging the core flow of the materials to such an extent that a transverse cross-section (FIG. 2) of the flowing materials may contain two or more layers in a radial material distribution A-B-A (or even A-B-A-B or more) of materials A and B in lengthy conduits. This. problem complicates the injection molding of preforms for blow molding containers meeting the aforementioned FDA requirements in multi-cavity mold constructions utilizing contiguously flowing material distribution systems.
Other prior art multi-cavity mold apparatus, that use coinjection molding to form multi-layered preforms, utilize molds in which a completely separate manifold system for each material, i.e. virgin and recycled, is used to separately convey that specific material to the singular cavities. The separate materials are then injected sequentially into the cavities utilizing a valve arrangement closely adjacent each cavity to control the flow from the separate manifolds into multi-orifice nozzles. Such arrangements result in molds that are expensive and complex.
It is an object of the present invention to provide a more distinct division between the recycled and pure materials being contiguously conveyed within the same conduit to the individual mold cavities in order to more accurately provide a substantially equivalent amount of molding materials to each cavity.
It is also an object of the present invention to provide a method and apparatus that yields a delivery method for a first and second material that delivers the respective materials at substantially the same temperature and at reduced costs while conveying substantially equal amounts of the respective materials at substantially simultaneous delivery times.
According to the invention, there is provided a multi-cavity coinjection mold for simultaneously producing a plurality of multi-layered articles comprising: a mold structure defining a plurality of mold cavities; a first supply source for supplying a first molding material; a second supply source for supplying a second molding material; a hot runner system in communication with said first and second supply sources for conveying timed metered quantities of said first and said second materials separately to a region proximate each cavity; and each said region comprising a contiguous gate and adjacent passage with a reciprocal pin closely housed in the passage for movement between a fully retracted position, in which the first and second materials are conveyed contiguously through said passage and said gate to the proximate cavity, and a gate closure position, in which the pin has ejected all of the first and second materials from the passage into the proximate cavity, the passage and gate having the same cross-section and size without restriction therebetween.
Also according to the invention, there is provided a multi-cavity coinjection mold for simultaneously producing a plurality of multi-layered articles comprising: a mold structure defining a plurality of mold cavities; a first supply source for supplying a first molding material; a second supply source for supplying a second molding material; a hot runner system in communication with said first and second supply sources for conveying said first and said second materials separately to a region proximate each cavity; a valve mechanism per cavity for receiving said first and said second materials from said hot runner system and for sequentially supplying desired quantities of said first and said second materials contiguously to a hot runner to a region proximate each cavity, wherein each hot runner communicates with a single cavity only; and each said region comprising a contiguous gate and adjacent passage with a reciprocal pin closely housed in the passage for movement between a fully retracted position, in which the first and second materials are conveyed contiguously through said passage and said gate to the proximate cavity, and a gate closure position, in which the pin has ejected all of the first and second materials from the passage into the proximate cavity, the passage and gate having the same cross-section and size without restriction therebetween.
Also according to the invention, there is provided a method of multi-cavity coinjection molding for simultaneously producing a plurality of multi-layered articles comprising: a) providing a mold structure defining a plurality of mold cavities; b) providing a first supply source for supplying a first molding material; c) providing a second supply source for supplying a second molding material; d) separately conveying said first and second materials through a hot runner system from said first and second supply sources to convey timed metered quantities of said first and said second materials separately to a region proximate each cavity; wherein each said region comprising a contiguous gate and adjacent passage with a reciprocal pin closely housed in the passage, the passage and gate having the same cross-section and size without restriction therebetween; and e) and moving the pin between a fully retracted position, in which the first and second materials are conveyed contiguously through said passage and said gate to the proximate cavity, and a gate closure position, in which the pin has ejected all of the first and second materials from the passage into the proximate cavity.